Among the most important advances in modern medical practice has been the adoption of a variety of minimally invasive procedures. Examples of such minimally invasive procedures include angioplasty, endoscopy, laparoscopy, arthroscopy and the like. Minimally invasive surgical procedures such as these can be distinguished from conventional open surgical procedures. In these minimally invasive procedures, access to a target site within the body of a patient is achieved through a relatively small incision, into which a tubular device (including a tube of a device) is inserted or introduced. The tubular device maintains the patency of the incision, while permitting access to the target site via the interior (lumen) of the device.
The tubular device can be configured for surgical use itself, or can be incorporated into another device. One example of the former is a balloon catheter, wherein the tube is configured as a catheter shaft, and carries an inflatable balloon on the shaft. Balloon catheters are useful, e.g., for performing angioplasty and for the deployment of an expandable stent and/or graft for preventing stenosis (closure) of a body passage, such as a blood vessel. Other examples of the former include a diagnostic, infusion or drainage catheter, in which the tubular device is configured as a catheter for the delivery of a diagnostic or therapeutic fluid to the patient, or for the removal of a fluid from the patient. Examples of devices including apparatus in addition to the tube are endoscopes, laparoscopes, arthroscopes and the like, as well as guide catheters and introducer sheaths (percutaneous or otherwise), through which a guide wire or other surgical device may be introduced into the patient.
To enhance torqueability and pushability, some catheters have included a braided reinforcement in the wall of the catheter shaft. However, braided catheters are relatively susceptible to kinking during use. Once a catheter kinks, fluid cannot pass through the lumen of its shaft, and the catheter becomes essentially useless. In balloon catheters, this prevents inflation of the catheter balloon. In addition, in other catheters, such as diagnostic, infusion and drainage catheters, prevention of fluid flow similarly interferes with their satisfactory use. As a result, the initially introduced catheter must be removed, and another catheter must be introduced into the patient and once again advanced through the vascular system to the narrowed site. This wastes time and increases the potential for trauma to the patient. To prevent kinking, some catheters include a coil embedded in the wall of the catheter shaft, rather than a braid. Although the presence of a coil inhibits kinking of the catheter, catheters having an embedded coil are undesirably susceptible to necking, that is, an undesirable reduction in its outer and/or inner diameter. In addition, utilizing a coil instead of a braid does not provide a great a degree of torqueability.
U.S. Pat. No. 6,939,337, assigned to the assignee herein, discloses a tubular medical device that includes a coil, such as a flat wire coil, in a stressed radially expanded condition, and a braid that extends over at least part of the coil. A bonding layer, formed from a polymer such as nylon or polyurethane, is positioned over and contacts the coil, or both the coil and the braid. The polymeric bonding layer maintains the coil in the stressed radially expanded condition, and is bonded to an inner liner, such as PTFE. By providing both a coil and a braid, the tubular device achieves some advantages attainable from each of these reinforcements. For example, the coil enables the device to better resist collapse, necking and kinking during use. The braid provides the device with enhanced pushability, trackability and torqueability. The '337 patent is incorporated by reference herein in its entirety.
Although the device of the '337 patent represents an improvement over prior art devices, it is desired to make still further improvements to such tubular devices to enhance their utility to an even greater degree than presently available. For example, it may be advantageous to have a splittable catheter shaft wall to facilitate deployment of a tubular medical device within a body vessel. During complete deployment of a stent or graft, the physician must retract the sheath from the stent over its entire length. This can be difficult for longer stents, e.g., over 140 mm, especially self-expanding stents, as the force of retraction and length of retraction are greater, making it relatively cumbersome to retract and requiring both hands to overcome the friction force.
United States Patent Application Publication No. 2007/0244540A1 to Pryor, which describes a delivery system for delivery a self-expanding stent, provides one solution for this problem. The delivery system includes a sheath with a breakaway having less structural integrity than the remainder to the sheath such that the sheath preferentially splits at the breakaway upon contact with a keel. However, the specific construct of the sheath in Pryor's delivery system is not described, and incorporating a sheath with a breakaway having less structural integrity than the remainder to the sheath reduces trackability, pushability and torqueability, as well as increase the probability of necking or kinking along the breakaway, during use of the sheath.
Thus, it would be desirable to provide an arrangement of a coil and/or a braid in a tubular device possessing sufficient trackability, pushability and torqueability, as well as being highly resistant to collapse, necking or kinking, during use. It would also be desirable if the tubular device is capable of being split longitudinally along its wall.